Republican presidential candidate and former Massachusetts Governor Mitt Romney pauses while speaking at a campaign rally in Denver, Colorado October 1, 2012 ahead of his first debate with U.S. President Barack Obama.

DENVER — Voters will have their chance to size up President Barack Obama and Republican presidential nominee Mitt Romney side-by-side, when both men take the stage at the University of Denver Wednesday night for their first of three debates.

And with Election Day just a month away, expectations and anticipation for tonight’s showdown at the University of Denver are mile high.

Romney, the Republican presidential hopeful, trails Obama in most polls, both nationally and in key battleground states. Tonight’s debate offers the challenger an opportunity to change the dynamics of the race and Romney is expected to take an aggressive posture in hopes of doing just that.

For his part, Obama will have to guard against his Republican opponent’s attacks – particularly on the anemic economy, and the administration’s response to a terrorist attack against a U.S. embassy in Libya last month – all while trying to illustrate the “contrast” between himself and Romney.

The stakes on Wednesday evening are especially high for Romney, who’s trailed Obama in most polls since each party’s national conventions concluded at the beginning of September. A series of missteps by Romney – involving his quick response to the incident in Libya and the revelation of secretly-recorded remarks by Romney seeming to write off 47 percent of voters, whom he called “dependent” upon government – have put the former Massachusetts governor and private equity titan in the unenviable position of having to make up ground versus Obama.

October’s three debates might be Romney’s last, best hope to accomplish that goal. Political observers typically look toward three moments in an election for a candidate to change the state of the campaign. The first two – choosing a running mate and the national convention – have come and gone for Romney.

That leaves this month’s debates – Wednesday in Denver, Oct. 11 in Hempstead, N.Y. and Oct. 22 in Boca Raton, Fla. – for Romney to make his argument.

The Republican nominee will look to deliver the kind of aggressive attacks on Obama for which his conservative supporters have clamored.

Several Romney voters at events here in Colorado preceding Wednesday’s showdown said they feared Romney currently trailed Obama. All of them said they wanted to see the GOP nominee come out swinging versus the president.

“I don’t think he has been tough enough,” said Caroline Peale, who attended Ann Romney’s event in Littleton on Tuesday afternoon. “He has so much ammunition. He doesn’t use it!”

Peggy Fulster, a self-described independent voter who decided for Romney in recent months, said: “I believe he's behind, but I think he can make up ground. I think a lot of people are sitting on the sidelines to see what happens in the debates.”

The risk for Romney could involve seeming too aggressive; he must straddle a delicate dividing line between criticizing the president and seeming petulant in a way that could turn off many swing voters.

Obama is sure to play defense at moments of the debate, which is moderated by Jim Lehrer of PBS. But the debate format is largely open-ended in a way that could maximize interactions between the candidates. As a result of a coin toss, Obama will deliver the first opening statement, and Romney will give the final remarks of the evening.

The president’s campaign has sought to play down expectations for Obama, emphasizing that the president hasn’t debated since the 2008 general election. Obama spent much of the last weekend and the first half of this week practicing for tonight’s matchup, huddling in Henderson, Nev. with senior staff and Massachusetts Sen. John Kerry, the 2004 Democratic presidential nominee who is playing the role of Romney in mock debates.

Obama, speaking a few days ago in Las Vegas, framed the debate as an opportunity to engage with Romney on issues of substance, playing down expectations and dismissing the notion of debate winners and losers.

“Gov. Romney, he's a good debater. I'm just okay,” the president said. “But what I'm most concerned about is having a serious discussion about what we need to do to keep the country growing and restore security for hardworking Americans. That's what people are going to be listening for. That's the debate that you deserve.”

Much of Obama’s campaign has focused on illustrating the differences between the two men, rather than embracing the model of an election that is effectively an up-or-down referendum on the president’s first term. Obama is likely this evening to continue in that vein, and has ample ammunition of his own to go after Romney. The Democrat’s campaign has turned Romney’s “47 percent” video into the subject of attack lines, and the president invokes Romney’s own low effective tax rate as evidence for why taxes should be reformed such that the wealthy pay a higher share of taxes.

Like Obama, Romney has spent a considerable amount of time preparing for these attacks and downplaying expectations. Romney’s team has pointed out that, despite the numerous primary debates earlier this cycle, the Republican presidential nominee hasn’t faced a Democratic opponent in about a decade, when he first ran for governor of Massachusetts.

“There’s going to be all the scoring of winning and losing, and you know, in my view, it’s not so much winning and losing or even the people themselves,” Romney said at a rally Monday evening in the Denver area.

Romney added: “I look forward to these debates. I’m delighted that we’re going to have three debates. It’ll be a conversation with the American people that will span almost an entire month.”

Ohio Sen. Rob Portman, a veteran of debate preparations for past Republican nominees, has taken the lead on playing Obama in practice sessions versus Romney. Portman traveled with Romney to Denver, and the two of them mostly worked privately on Tuesday in anticipation of tonight’s debate.

Would-be first lady Ann Romney pronounced her husband “excited” and “focused” in a rally Tuesday afternoon.

But whether there are that many undecided voters remaining on the sideline is another question. The challenge – for both candidates – could end up involving the number of voters who appear to have already determined their vote, making it more difficult than usual for either Romney or Obama to sway voters with a strong debate performance.

Tuesday’s NBC News-Wall Street Journal poll found that most voters, 60 percent, called the debate either "just somewhat important" or "not at all important."

Video: Romney must boost appeal with working class voters

>>president obama
heads to
colorado
today.
mitt romney
has been here since monday night. with me now is former
colorado governor
billowens. the second of three
colorado
governors i have on my show today. let me start with the same question i asked governor hickenlooper. why is
colorado
a
swing state
? what do you tell friends and families and colleagues when they ask what makes
colorado
such a right down the middle state?

>>it is one of the best educated states in the country in terms of college graduates it is the best educated state in the country. we really are a microcosm of the country. a lot of coloradoens came from other states. and so it's a nice place to battle out the country's elections. and as you probably pointed out earlier we have gone all sorts of ways in
presidential elections
. we have elected democratic governors. i think the coloradoens take a look at the candidate and vote for the person they think will do the best job for
colorado
and the country.

>>it seems to me in watching what i feel like the conversation
colorado
voters are having with each other is that the president thinks women voters and social issues are the key to the reelection and the
romney
campaign thinks talking about the deficit is a winner here. what say you? are both on the right track to get to 50?

>>i think it depends on which base the two parties are trying to get out. obviously the
democratic party
with its so-called war on women is trying to make sure it gets the turnout from that element. and my party is looking i think more broadly at the fact that the economy effects men and women. the deficit effects men and women young and old. i would suggest that my party and
mitt romney
are actually waging a campaign that is trying to address real issues as opposed to issues that really haven't proven to be very operative in the past, social issues and abortion, for example. those are wedge issues that drive your base up if you are a democratic candidate.

>>wasn't the issue of abortion the reason
michael bennett
got reelected to a
full term
?

>>there were a number of reasons. republican presidents and republican congresss and republican governors and republican legislatures haven't taken away the right to abortion anywhere in the country. it is pretty much a
straw argument
that it is a constitutionalal right addressed around the edges. what the
romney
campaign believes and what
mitt romney
believes is that the future of the country depends on the economy, depends on getting this deficit under control and really starting to get america growing again. more americans are unemployed today than when
barack obama
took office. whose fault is that? you raised good points but i am comfortable with governor
romney
's position.

>>if you are giving advice your advice would be what?

>>i won hispanics in
colorado
in my second race. i think governor
romney
's focus on the economy are
hispanic americans
are impacted perhaps even more than the rest by this softer economy. and so i would do what governor
romney
has been doing and that is continue to address the base issues. this is an election that has to look at how well we have done over the last four years.
president obama
was elected with this hope and this vision for change. and we have seen change actually for the worst. i think it is very fair to look at his record and say here is what he said four years ago and here is what he hasn't accomplished. so obviously a lot of tonight is going to be about
president obama
's record, just since four years ago
president obama
was looking back at the record of those he wanted to replace.